1. Field of the Invention
The present invention concerns a power tool, preferably a hammer drill or a chipping hammer comprising a lubricated transmission arranged in a sealed transmission box, in particular in an air-tight transmission box, wherein the transmission box is in fluid connection with the atmosphere via a venting channel, and an air-permeable sealing element arranged in the venting channel.
2. Description of the Related Art
Such a power tool is, for example, known from EP 1 252 976 A1, wherein the transmission box is open towards the atmosphere via a narrow channel and a filter connecting to this channel. The filter element may, for example, be a felt.
If the transmission is lubricated by oil or an oil-like lubricant, there is the danger that the felt soaks up the oil through capillary action and that the transmission starts to leak after a short time (oil leakage by capillary action). A similar problem arises also when using grease or grease-like lubricants. Here, the felt works similar to a sieve and separates the grease into its components. The base oil is soaked up by the felt through capillary action, whereas the soaps from the grease remain sticking on the surface of the felt and form a thick layer. This layer seals the felt so that a further loss of lubricant is avoided but at the same time no more venting of the transmission housing is warranted. However, the venting is necessary because the air pressure within the transmission housing of the hammer drill or chipping hammer is subject to continuous oscillations due to changes in temperature and the operation of the hammer mechanism, and a pressure compensation with the atmosphere has to be provided.